It's important to measure your brake rotor wear
every 10,000 miles or at the very least every time you change your brake pads.
You want to use a micro measuring caliper to determine your brake rotor thickness. For
example, a new brake rotor with a thickness of 10mm is required to be replaced
or turned at 9mm, meaning that your naked eye has to detect 1mm of rotor wear.
Kinda impossible.

In order to get an accurate measurement for the amount of brake rotor wear we depend
on our trusty micrometer. Prepare your car so you can remove the wheel.

With the wheel removed, you will have clear
access to the rotor for you to make accurate measurements. There are several
types of micrometers and measuring calipers so you want to make sure you
caliper can measure to the tenth of a millimeter.

Next, you simply measure the thickness in at
least three different spots of the brake rotor. Make sure to write down your
measurements and you may get a few small variations. It helps to get at least
4-5 different measurements and to take the average of that.

Next, take a look at the brake rotor center hat.
This is the portion that doesn't get exposed to the brake pad. You will
normally find your minimum rotor thickness stamped there. It may be faint, but
it's usually there. In some cases it may be located on the outer edge of the
rotor.

Tip: Keep in mind that you want to avoid
measuring too close to the inside/outside of the rotor, as the actual brake pad
doesn't contact those edges. Also, for slotted rotors stay away from measuring the
slots, as those will skew the results. Same goes with dimpled/cross-drilled
rotors. Keep clear of measuring the holes.